PUBLISHED VERSION
Fusion alpha-particle diagnostics for DT experiments on the Joint European Torus
Kiptily V G, Beaumont P, Belli F, Cecil F E, Conroy S, Craciunescu T, Garcia-Munoz M, Curuia M,
Darrow D, Ericsson G, Fernandes A M, Giacomelli L, Gorini V, Murari A, Nocente M, Pereira R C, Perez
Von Thun C, Popovichev S, Riva M, Santala M, Soare S, Sousa J, Syme D B, Tardocchi M, Zoita V L,
Chugunov I N, Gin D B, Khilkevich E, Shevelev A E, Goloborod'ko V, Sharapov S E, Voitsekhovitch I,
Yavorskij V, JET-EFDA contributors
© 2014 UNITED KINGDOM ATOMIC ENERGY AUTHORITY
This article may be downloaded for personal use only. Any other use requires prior permission of
the author and the American Institute of Physics. The following article appeared in Fusion Reactor
Diagnostics: Proceedings of the International Conference, 9-13 September 2013, Villa Monastero,
Varenna, Italy. AIP Conf. Proc. 1612 , 87 (2014) and may be found at :
http://dx.doi.org/10.1063/1.4894029
Fusion alpha-particle diagnostics for DT experiments on the joint European torus
V. G. Kiptily, P. Beaumont, F. Belli, F. E. Cecil, S. Conroy, T. Craciunescu, M. Garcia-Munoz, M. Curuia, D.
Darrow, G. Ericsson, A. M. Fernandes, L. Giacomelli, Gorini, A. Murari, M. Nocente, R. C. Pereira, C. Perez Von
Thun, S. Popovichev, M. Riva, M. Santala, S. Soare, J. Sousa, D. B. Syme, M. Tardocchi, V. L. Zoita, I. N.
Chugunov, D. B. Gin, E. Khilkevich, A. E. Shevelev, V. Goloborod'ko, S. E. Sharapov, I. Voitsekhovitch, V.
Yavorskij, and JET-EFDA contributors
Citation: AIP Conference Proceedings 1612, 87 (2014); doi: 10.1063/1.4894029
View online: http://dx.doi.org/10.1063/1.4894029
View Table of Contents: http://scitation.aip.org/content/aip/proceeding/aipcp/1612?ver=pdfcov
Published by the AIP Publishing
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Fusion Alpha-Particle Diagnostics for DT Experiments
on the Joint European Torus
V.G. Kiptilya, P. Beaumonta, F. Bellib, F.E. Cecilc, S. Conroyd, T. Craciunescue, M.
Garcia-Munozf, M. Curuiag, D. Darrowh, G. Ericssond, A.M. Fernandesi, L.
Giacomellil, Gorinil,m, A. Murarin,o, M. Nocentel,m, R.C. Pereirai, C. Perez Von
Thunf,o, S. Popovicheva, M. Rivac, M. Santalap, S. Soareg, J. Sousai, D.B. Symea, M.
Tardocchim, V.L. Zoitae,o, I.N. Chugunovq, D.B. Ginq, E. Khilkevichq, A.E.
Shevelevq,V. Goloborod’kor,s, S.E. Sharapova, I. Voitsekhovitch1, V. Yavorskijr,s and
JET-EFDA contributorst
JET-EFDA, Culham Science Centre, OX14 3DB, Abingdon, UK
Euratom / CCFE Fusion Association, Culham Science Centre, Abingdon, Oxon, United Kingdom
b
Associazione Euratom -ENEA sulla Fusione, C.R. Frascati, C.P. 65, Frascati, Italy
c
Colorado School of Mines, Golden, CO, USA
d
Department of Physics and Astronomy, Uppsala University, BOX 516, Uppsala, Sweden
e
Association Euratom -MEdC, National Institute for Laser, Plasma and Radiation Physics, Romania
f
Max-Planck-Institut f¨ur Plasmaphysik, EURATOM-Association IPP, Garching, D-85748, Germany
g
Association Euratom -MEdC, National Institute for Cryogenics and Isotopic Technology, Romania
h
Princeton Plasma Physics Lab, Princeton NJ, USA
i
Euratom/IST Fusion Association, Centro de Fusão Nuclear, 1049-001 Lisboa, Portugal
l
CNISM, Dipartimento di Fisica, Universita Milano-Bicocca, Milano, Italy
m
Associazione Euratom -ENEA sulla Fusione, IFP Milano, Italy
n
Consorzio RFX - Associazione Euratom-Enea sulla Fusione, I-35127 Padova, Italy
o
EFDA Close Support Unit, Culham Science Centre, Culham, OX14 3DB, UK
p
Association Euratom-Tekes, Helsinki Univ. of Technology, P.O.Box 2200, FIN-02015 HUT, Finland
q
A.F. Ioffe Physico-Thechnical Institute, 194021 St. Petersburg, Russia
r
Euratom/OEAW Association, Institute for Theoretical Physics, University of Innsbruck, Austria
s
Institute for Nuclear Research, Kiev, Ukraine
t
See the Appendix of F. Romanelli et al., Proceedings of the 24 th IAEA FEC 2012, San Diego, USA
a
Abstract. JET equipped with ITER-like wall (a beryllium wall and a tungsten divertor) can provide auxiliary heating
with power up to 35MW, producing a significant population of D-particles in DT operation. The direct measurements of
alphas are very difficult and D-particle studies require a significant development of dedicated diagnostics. JET now has
an excellent set of confined and lost fast particle diagnostics for measuring the α-particle source and its evolution in space
and time, α-particle energy distribution, and α-particle losses. This paper describes how the above mentioned JET
diagnostic systems could be used for D-particle measurements, and what options exist for keeping the essential D-particle
diagnostics functioning well in the presence of intense DT neutron flux. Also, α-particle diagnostics for ITER are
discussed.
Keywords: tokamak, DT plasmas, alpha-particles, diagnostics
PACS: 52.55.Fa, 52.55.Pi, 52.70.La
INTRODUCTION
The nuclear fusion reaction between deuterium and tritium, D(T,n)4He is a main source of energy in future
thermonuclear reactors. Charged fusion products of this reaction, D-particles (4He-ions), which are born with an
average energy of 3.5 MeV and transfer the energy to the thermal plasma during their slowing down, will provide
the power for the self-sustained DT-plasma burn. Adequate confinement of D-particles is essential to provide
Fusion Reactor Diagnostics
AIP Conf. Proc. 1612, 87-92 (2014); doi: 10.1063/1.4894029
2014 AIP Publishing LLC 978-0-7354-1248-4/$30.00
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efficient heating of the bulk plasma and steady burning of a reactor plasma. Therefore investigation of D-particles
behaviour will be a priority task for the planned deuterium- tritium experiments on JET in order to understand the
main mechanisms of their slowing down, redistribution and losses and to develop optimal plasma scenarios.
Today’s JET machine has been equipped with a beryllium wall, a tungsten divertor (ITER-like wall) and
enhanced auxiliary heating systems, including NBI with power up to 35MW. Therefore possible future deuteriumtritium experiments on JET are expected to produce significant population of D-particles at plasma parameters
approaching as closely as possible the ITER values, so the experiments will give great opportunities to study fusion
alphas. The confinement of fast particles produced in fusion reactions is of crucial importance for future fusion
devices like ITER and DEMO.
What do we want to measure in the next deuterium-tritium experiments on JET? First of all these are the
deuterium-tritium fusion reaction rate and spatial D-particle source profile. Measurement of the slowing down,
redistribution and losses of D-particles is another high priority task for optimisation of the plasma scenarios and
assessments of MHD effects on the DT plasma performance.
The first full scale DT-experiment on JET in 1997 (DTE1) has shown that direct measurements of alphas are
very difficult. Alpha-particle studies require a significant development of dedicated diagnostics. Since DTE1, JET
has been gradually building up dedicated fast ion diagnostics, which have been tested step-by-step in a variety of
plasma scenarios such as ICRH accelerated 4He-ions and fusion born α-particles in Trace Tritium Experiments
(TTE) in 2003. JET has now excellent set of confined and lost α-particle diagnostics, which comprise of γ-ray
spectrometry for measuring energy distribution of fast ions; 2D neutron/γ-ray camera for tomographic reconstruction
of the α-particle source and the temporal evolution of its spatial profile; a fast ion loss detector (Scintillator Probe)
with energy and pitch-angle resolutions and a set of Faraday Cups with poloidal, radial, and energy resolution for
measuring lost alphas. For operating all these diagnostics at the high DT neutron fluxes expected in future highpower DT campaign, specific improvements are proposed for some of the diagnostic tools.
This paper describes how the above mentioned JET diagnostic systems could be used for D-particle
measurements, and what options exist for keeping the essential D-particle diagnostics functioning well in the
presence of intense DT neutron flux. It is organized as follows. The fusion D-particle source measurements on JET
are described in section 2. The confined D-particle diagnostics are presented in section 3. Section 4 is devoted to the
escaped D-particle measurements.
FUSION ALPHA-PARTICLE SOURCE MEASUREMENTS
There are two major fusion reactions that produce energetic D-particles,
D T o4He(3.5MeV ) n(14.1MeV )
and
D3Heo4He(3.7MeV ) p(14.7MeV ) .
For the first one, which is reactor relevant, 14-MeV neutron measurement is a main tool for the DT fusion power
and D-particle source profile measurements. Measurements of the neutron source profile (which is identical to the
alpha-particle source) provide the principal technique for studying fast fuel ion distributions, which are produced
non-symmetrically on flux surfaces by NBI and ICRH. This is very important in reactors and plasmas influenced by
magneto-hydrodynamic (MHD) instabilities.
There is another instrument for D-particle source profile measurements. The detection of 17-MeV gammas from
a weak branch of the DT fusion reaction
D T o5He J (16.85MeV ) ,
can provide the same information as 14-MeV neutrons. A disadvantage of this method is a low cross-section of the
branch σγ/σn ~ 0.005%. However, efficient γ-ray detectors allow information to be obtained with required time
resolution for high performance plasmas. This tool has been tested on JET in experiments with 3He-minority ICRF
heating of deuterium plasmas. The similar γ-rays with energy ~16 MeV from a weak branch of D3He fusion reaction
(σγ/σp ~ 0.005%),
D3Heo5Li J (16.39MeV )
were detected with an efficient scintillation detector and γ-ray energy spectra have been recorded during discharges.
In both reactions peaks related to ground states are broad; widths are ΓDT ~ 0.6 MeV and ΓD3He ~ 1.6 MeV. There is a
second peak related to the first excited state with Γ ~ 5 MeV in the D3He reaction.
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The JET neutron/gamma camera is a unique instrument for imaging of the noncircular plasma neutron/gamma
source [1-6]. It consists of two fan-like multi-collimator detector arrays [7]. A nine-channel camera is positioned
above the vertical port to view downward through the plasma, while a ten-channel assembly views horizontally from
the side. The collimation can be remotely adjusted by use of two pairs of rotational steel cylinders. Each channel is
equipped with a set of three different detectors: a NE213 liquid organic scintillator with digital data acquisition
system, which allows pulse shape discrimination for simultaneous measurement of 2.5 MeV DD neutrons, 14-MeV
DT neutrons, and γ-rays; a BC418 plastic scintillation detector for measurement of 14-MeV D-T neutrons, which is
located in front of the NE213 scintillator and is coupled to a photomultiplier tube via a light guide; and a CsI(Tl)
photodiode with a diameter of 20 mm and a height of 15 mm for measuring the HXR/γ-ray emission in the range
between 0.2 and 6 MeV. All neutron detectors are absolutely calibrated for both DD and DT neutrons.
CONFINED ALPHA-PARTICLE DIAGNOSTICS
Nuclear reaction J-ray diagnosis is one of the important techniques used on the JET tokamak for studying
confined fast ions [1-6]. The intense J-ray emission is produced in JET plasmas when fast ions (ICRF-driven ions,
fusion products, NBI-injected ions) react either with fuel ions or with the main plasma impurities such as carbon and
beryllium. Gamma-ray energy spectra are recorded with collimated spectrometers, while the J-ray emission spatial
2D-profiles are measured with the JET neutron/gamma camera. Together, these provide information on the spatial
distribution of fast ions and fast ion tail-temperature.
For identification of the fast ions, which exist in the plasma and produce the observed J-ray emission, and in
order to assess the effective tail temperatures of these fast ions, the J-ray spectrum modelling code, GAMMOD [3]
is used. This code is based on the known nuclear reaction cross-sections and it contains information on about one
hundred J-ray transitions in the final nuclei of the low-Z impurity reactions. It also includes the J-ray response
function of the BGO-spectrometer. A Maxwellian energy distribution is used to describe the line-of-sight averaged
tail of ICRH-accelerated ions. The GAMMOD code analysis gives the effective tail temperatures, the fast ion
concentrations and the contribution to the neutron yield from the fast particle-induced reactions.
On JET, the D-particle diagnostic technique is based on the nuclear reaction 9Be(D,nJ)12C between confined Dparticles and the beryllium impurity typically present in the plasma [8, 9]. The J-radiation due to the reaction
9
Be(D,nJ)12C has been observed for the first time in JET experiments with the third harmonic ICRF heating of 4He
beam ions in a 4He plasma [4,10] and in deuterium plasmas with short T-NBI blips for D-particles [11]. These
experiments on JET showed that an improvement of the diagnostics is needed for the measurements in the high
neutron yield DT discharges to demonstrate the capabilities of J-ray diagnostics for burning plasma physics in future
reactors.
Gamma-ray spectrometers
Gamma-ray energy spectra are measured on JET with five independent devices, one with a tangential, and four with
vertical lines of sight, through the plasma centre. The tangential spectrometer is a calibrated bismuth germanate
(BGO) scintillation detector with a diameter of 75 mm and a height of 75 mm. It is located in a shielded bunker,
which views the plasma quasi-tangentially. In order to reduce the neutron flux and the J-ray background, the front
collimator is filled to a depth of 500 mm with polythene. Behind the scintillation detector, there is an additional 500
mm long dump of polythene and a 1000-mm long steel plug. The detector's line of sight lies in a horizontal plane
about 30 cm below the plasma magnetic axis. The J-ray spectra are continuously recorded in all JET discharges over
the energy range 1-28 MeV, with energy resolution of about 4% at 10 MeV.
A pair of neutron/J-ray collimators working in a tandem configuration has been installed for background
reduction and precise characterization of the tangential J-ray spectrometer field of view (FoV) [12, 13]. The tandem
collimators provide shielding factors CDD ≈ 2x10-3 for 2.45 MeV neutrons and Cγ ≈ 10-3 for 9 MeV J-ray.
A similar collimator system was designed for DT experiments: CDT ≈ 2x10-3 for 14 MeV neutrons and Cγ ≈ 10-3
for 9 MeV J-ray. This system provides necessary conditions for the operation of diagnostics in high performance
DD and DT discharges. However, this is not sufficient to diagnose the confined D-particles. There is a proposal of
further upgrade of shielding and neutron attenuators. It consists of the additional neutron and J-ray shields at the
entrance of the bunker and replacement of polythene attenuators in front of the detector by LiH attenuators. Also,
the detector change is considered.
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The feasibility of J-ray measurements depends on efficiency of the neutron suppression. Also, it is important to
avoid carbon-containing materials in the neutron attenuator because of inelastic scattering neutrons with energy
exceeding 5 MeV, 12C(n,n’J)12C, leads to the unwelcome background of 4.44-MeV J rays. The best neutron
attenuator is 6LiH, but LiH with a natural Li composition could be used as well. It is compact, effective and well
transparent to MeV J-rays. It does not produce interfering J-rays in the high-energy range. A 30-cm sample of the
6
LiH-filter reduces 2.5-MeV neutron flux a900 times and the 15-MeV neutron flux a30 times [14]. The attenuator
has been tested in JET experiments with deuterium plasmas [15]. Assessments of the J-ray background reduction in
the energy range below 3 MeV gave a factor of 100. A small reduction of the spectra (factor of 2) was found in the
energy range above 3 MeV, which is defined by J-ray transparency of the 6LiH-attenuator. Further tests in DT
discharges will prove the full capability of 6LiH-attenuators as an essential component of the J-ray diagnostic system
in ITER.
Another four spectrometers are viewing the plasma centre vertically through 2-m collimators. Three of them, a
NaI(Tl), LaBr3(Ce) scintillators and HpGe-detector (a high purity Ge-detector) placed on a remotely controlled
slider are sharing the same line of sight (LoS). Depending on the experimental task one of the detectors is moved in
the working position. A second slider with polythene slabs is used for choosing optimal neutron/J-ray attenuation.
The J-ray spectra are continuously recorded in all JET discharges over the energy range 1-20 MeV. The fourth
detector, LaBr3(Ce) scintillator installed at another toroidal position is permanently recording spectra viewing the
plasma centre through 30-cm 6LiH attenuator. For the DT operation an additional 30-cm attenuator is considered.
The best detector for the DT operation is a fast high-Z heavy scintillator LaBr3(Ce), known as "BriLanCe". It has
short decay times of ~20 ns, high photons yield and practically insensitive to neutrons. The detector crystal is
coupled to a photomultiplier tube (PMT) designed to allow operations at count rates up to 2 MHz. High rate
capability is enabled by a dedicated pulse digitization data acquisition system based on the ATCA platform with a
sampling frequency up to 400 MSPS and a nominal 14-bit resolution [16]. Their outstanding properties open a
possibility to extend the counting rate limit beyond 5 MHz, and at the same time to improve the energy resolution
for J-ray spectrometry in the range 2 - 30 MeV. A test on an accelerator [17] has demonstrated that spectra can be
measured in the MHz range without significant degradation of the energy resolution up to 2.6 MHz (~2% at 3 MeV).
Measurements at higher counting rates up to 4.4 MHz showed just a modest broadening of the energy resolution
(0.2% increase at 3MeV). This spectrometry system meets the requirements of D-particle diagnostics on ITER. It is
considered replacing the tangential BGO detector by the scintillator. Replacement of the tangential BGO detector by
a LaBr3(Ce) scintillator is being considered.
The use of HpGe-detector will be important for an experimental test of another D-particle diagnostic. Proposed
two decades ago [8, 9] it is based on the Doppler shape analysis (DSA) of the 4.44MeV γ -ray line related to the
nuclear reaction 9Be(α,nγ)12C between α-particles and the beryllium, which is a main impurity in JET plasmas.
Contrary to the radiation capture reactions, in this type of nuclear reaction the Doppler effect is the main mechanism
of peak broadening. In experiments with the 3rd harmonic ICRH heating of a 4He neutral beam (Z=3Z4He) in 4He
plasmas, J-radiation due to the reaction 9Be(D,nJ)12C has been observed and DSA of 4.44MeV γ-ray line carried out
for the first time [18, 19]. The use of DSA technique requires well known differential nuclear cross-sections as well
as FoV and fast ion distribution modelling. A sophisticated DSA of characteristic γ-ray emission peaks from the
reaction 12C(3He,pJ)13C measured in D3He plasmas with ion cyclotron resonance heating tuned to the fundamental
harmonic of 3He minority has been done [20].
In the DT experiments this detector can be used with a high level attenuation of the neutron flux in the LoS. To
provide the same working conditions as in the case of deuterium operations the attenuation of 14-MeV neutrons
should be ~10-4 in the high performance DT discharge. It means the LiH attenuator has to have thickness ~80 cm.
Gamma-ray camera
The imaging of fast ions with γ -ray camera has been very successfully applied so far in ICRH experiments [3-6].
The extension of these diagnostics to high fusion performance (high neutron yield) discharges requires an adequate
reduction of both neutron flux and the neutron-induced gamma-ray background. To this end a set of three neutron
attenuators of different shape and attenuation length have been designed, constructed and installed for the horizontal
and vertical cameras [21, 22]. The radiation performance of the neutron attenuators has been modeled by
neutron/photon transport calculations. The attenuators have a different design for the horizontal and vertical
cameras. A quasi-crescent shaped neutron attenuator has been chosen for the horizontal camera with an attenuation
factor for DD-neutrons kDD = 10-2. For the vertical camera there are two quasi-trapezoid shaped neutron attenuators,
with different attenuation lengths: a short version (kDD = 10-2), to be used together with the horizontal attenuator for
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deuterium discharges and a long version (kDD = 10-4) to be used for high performance DD and DT discharges (kDT =
6.7x10-2). All three neutron attenuators consist of a metal casing filled with pure light water as attenuating material.
They have to be moved out of the detector line of sight when the camera diagnostics are used for neutron
measurements. The system operates in a harsh electromagnetic environment therefore the remote steering and
control are based on pneumatic components.
With a long vertical attenuator the γ-ray measurements will be possible in DT discharges with neutron rate up to
5x1017 n/s. This is very important diagnostic improvement, which will be useful for the confined D-particle studies
in scenarios with ICRF heating. However, the CsI-detectors used in the camera are very slow and cannot provide
reliable information on the spatial re-distribution of confined D-particles due to a pile-up effect at expected high
count rates. It is considered replacing them by LaBr3(Ce) detectors of the same size, which can work at several MHz
count rates.
In the case of ITER, the slowed down 1-MeV beam deuterons will give rise to gammas from the 9Be(d,nJ)10B
and 9Be(d,pJ)10Be reactions, whereas the fusion alphas with energies around the 2-MeV resonance in the
9
Be(D,nJ)12C reaction will produce 4.44-MeV gammas. Furthermore, the source of fusion D-particles can be
obtained by measuring the 17-MeV gammas from the D(T,J)5He reaction. Using J-ray spectrometers in every
channel of the ITER Radial Camera, D-particle slowing down profiles could be measured with the technique
successfully tested in JET Trace Tritium Experiments [11]. Simultaneous measurements of the NBI power
deposition and D-particle slowing down profiles are very important for the optimisation of different plasma
scenarios and understanding of the fast-ion confinement physics.
ESCAPED ALPHA-PARTICLE DIAGNOSTICS
JET is exceptionally well equipped for studying fast ion confinement and losses. It is capable of simultaneously
measuring different species of confined fast ions, including D-particles using the γ-ray diagnostics, and equipped
with lost ion diagnostics: a thin foil Faraday cup (FC) array [23] and a scintillator probe (SP) [24, 25].
The Faraday Cup array detects the current of fast ions at multiple poloidal locations, with a dynamic range from
10 nA/cm2 to 10 mA/cm2 at a temporal resolution of 1 ms. The detectable range of D-particle energies is about 1–5
MeV. The energy resolution for 3.5 MeV D-particles is estimated to be about 15%–50%. The array consists of nine
detectors spread over five poloidal locations (Z) between 22 cm and 80 cm below the midplane. Radially, the
detectors are equally spaced on three locations between 25 and 85 mm behind the adjacent poloidal limiter. Each
detector consists of at least four 75u25 mm2 Ni foils (2.5 Pm in eight of the detectors and 1.0 Pm in the ninth),
which are separated by insulating mica foils. Depending on its energy, a particle can pass through a certain number
of foils before it is stopped in one foil, thus causing a current signal. The detection of the temporal evolution of the
current signals in all foils in the radially and poloidally distributed detectors will allow mapping particle energies at
different locations.
The Faraday Cups are resistant to neutron and γ-ray radiations. At the n/γ flux ~1013 cm-2 s-1 the predicted
background foil currents are In~0.1 nA/cm2 and Iγ~0.01 nA/cm2 that is much less than current produced due to Dparticle losses ID~100 nA/cm2.
The Scintillator Probe, which is located about 28 cm below the mid-plane of the JET torus outside the plasma,
detects lost ions and provides information on the lost ion pitch angle T=arccos(v║/v) with 5% resolution in the range
35° - 85° and gyro-radius between 3cm and 14cm with 15% resolution. The underlying principle of scintillator
measurements is the emission of light by a scintillating material after a particle strikes this material. Selection
criteria for the particles that hit the scintillator are introduced by using a set of collimators within the magnetic field
of JET. An optical arrangement within the scintillator probe is used to transfer the light emitted by the scintillator
through a coherent fibre bundle towards a charge-coupled device (CCD) camera and a photomultiplier (PMT) 4x4
array. The 128x256 pixel CCD camera used in SP can provide 20-kHz snapshots of the light intensity on the pitchangle – gyro-radius grid calculated with the EfipDesign code [26]. A fast 20-μm scintillator with decay time 0.5μs is
installed in SP, which is radiation resistant. An electrically-heated hose for restoration of the fibre optic bundle
degradation will be used.
Fusion alpha-particle [5, 27, 28] and 4He-ion [29] losses have been measured with FC and SP in JET
experiments with 3He-minority heating of deuterium plasmas and the 3rd harmonic ICRH (Z=3Z4He) acceleration of
4
He-beam ions in 4He plasmas. The 4.44-MeV J-radiation due to the reaction 9Be(D,nJ)12C was observed that means
D-particles/4He-ions had energies in excess of 2 MeV. Also the measured 17-MeV γ-rays of the D(3He,γ)5Li reaction
indicate the rate of the D(3He,p)4He fusion reaction, which produces D-particles at 3.6 MeV and protons at 15 MeV
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and in most of the discharges this rate was rather high. It was found that the fusion D-particles more frequently
escape from the plasma during Alfvén cascade and tornado mode activity. There are two possible reasons for the
observed effect of the loss dependence on the Alfvénic activity. First, ICRH-accelerated 3He ions with tail
temperature of few hundred keV, which are the source for D( 3He,p)4He fusion reaction, may be so strongly redistributed by a resonant interaction with the Alfvénic modes, that the re-distribution of 3He affects the profiles of Dparticles born in D(3He,p)4He fusion reactions. Second, the perturbed magnetic field associated with the Alfvénic
modes, may directly affect the fusion-born D-particles in the region of the phase-space close to the boundary
between confined and unconfined particles.
There is another γ-ray technique proposed to measure escaped D-particles [9], which is ITER relevant. It is based
on the same nuclear reaction 9Be(D,nJ)12C as for confined particle diagnosing. In this case, escaped D-particles with
energies in excess of 2 MeV, interacting with beryllium wall or a specially installed target, give rise to 4.44-MeV Jradiation. Measurements of the radiation provide the rate of fast D-particle losses. It is important that the detector
FoV do not intersect the plasma core, which is a source of 4.44-MeV J-emission produced by confined D-particles.
This lost D-particle diagnostic could be tested on JET during the DT experiments. A thick beryllium target with 500600cm2 surface installed in FoV of a gamma-camera detector could provide the required intensity of the 4.44-MeV
J-radiation for D-particle loss monitoring in DT experiments.
ACKNOWLEDGMENTS
This work, supported by the European Communities under the contract of Association between EURATOM and
CCFE, was carried out within the framework of the European Fusion Development Agreement. The views and
opinions expressed herein do not necessarily reflect those of the European Commission. This work was also partfunded by the RCUK Energy Programme under grant EP/I501045.
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